This application relates to transurethral hypothermia apparatus. It relates more particularly to a dual mode (i.e heating and sensing) transurethral microwave warming apparatus.
It is well known that heat can be used to reduce an enlarged prostate. Benign prostatic hyperplasia (BPH) is a common disease among aging men that may lead to several complications such as urinary tract infection, acute urinary retention or uremia. In the U.S. alone, there are approximately 400,000 transurethral resection procedures performed each year involving general anesthesia and hospitalization to treat the above problem. Many patients are poor surgical risks due to age and possible co-existing health problems.
Microwave hyperthermia appears to be a practical alternative to transurethral resection for the prostate, the usual surgical procedure. Microwave transurethral hyperthermia involves insertion of a small catheter, including a microwave antenna, into the bladder via the urethra. This procedure can be performed in an outpatient basis without the need for general anesthesia.
It is also well known that hyperthermia can be used as an adjunct to ionizing radiation as a treatment for a malignant disease. According to the American Cancer Society, cancer of the prostate is currently the second most lethal cancer in American men. Numerous studies have demonstrated that microwave hyperthermia can be a valuable adjunct to radiation therapy in the treatment of prostrate cancer. The combination of microwave heating and ionizing radiation is far more effective than either of the treatments alone, thereby significantly reducing the level of ionizing radiation required. However, the success of hypothermia rests on the ability to effectively heat the tumor volume to therapeutic temperatures without causing damage to the adjacent normal tissue.
Conventional transurethral catheters used in prostrate applications have multiple lumens with at least one lumen dedicated to the microwave antenna or applicator. The catheter also has other working lumens used for coolant, drainage, temperature probes and inflation fluid, e.g. air, for inflating a balloon at the tip of the catheter for positioning the catheter after insertion.
FIG. 5 of the drawings shows a conventional transurethral catheter used in prostate applications. It includes an elongated probe or body 10 having a plurality of length-wise lumens. There is a central lumen 12 with a counterbore 12a for accommodating a coaxial cable 14. The cable""s center conductor extends to the distal end of lumen 12 and constitutes an antenna 16. Probe 10 also has a second, generally U-shaped lumen 18 whose legs 18a are located radially outboard lumen 12 and which provides a path for the circulation of a coolant fluid through the probe to cool the external surfaces of the probe. As noted previously, catheters of this type usually include a balloon 22 adjacent to the distal end of probe 10. Therefore, an additional lumen 24 extends along probe 10 to carry the inflation fluid to the balloon. Various other working lumens may extend along probe 10. For example, there may be a lumen 25 which runs the length of the probe and is used for the drainage of body fluids after the catheter is inserted in a patient. There may also be a lumen indicated at 26 for accommodating one or more heat sensors 30 such as a thermocouple, thermister or fiberoptic device. All of the working lumens extend to the proximal end of the probe 10 where they connect to tubes which lead to various units supporting the above-described functions of the lumens. The FIG. 5 catheter is fully described in U.S. Pat. No. 5,234,004.
As seen from the above patent, with the balloon 22 in its deflated condition shown in solid lines in FIG. 5, the distal end 10a of the probe 10 may be inserted into the urethra up to the level of the tissue to be treated by the thermal affect at which level the balloon 22 reaches the patient""s bladder. Thus, after inflating the balloon by flowing an inflation fluid such as air through lumen 24 so that the balloon expands as shown in phantom in FIG. 5, the catheter is locked in the bladder neck thereby achieving a precise positioning of antenna 16 relative to the patient""s prostate which surrounds the urethra, that position being maintained during the entire treatment.
After probe 10 has been positioned thusly, microwave power may be delivered via cable 14 to antenna 16 which produces a radiation pattern that heats the tissue near the probe. Preferably, a coolant is circulated through lumen 18 in order to lower the surface temperature of probe 10 to prevent overheating the tissue right next to the probe. As described in the above patent, a heat sensor 30 may be present in lumen 26 for sensing the temperature on or inside probe 10. The output from the sensor can then be used to control the power delivered to antenna 16 so that the tissue to be subjected to the thermal effect is heated to within a selected temperature range.
Transurethral catheters of the above type are disadvantaged in that the fluid-carrying lumens 18, 24 and 25 are located between antenna 16 and the tissue surrounding probe 10. Resultantly, the various fluids flowing through those lumens perturb the antenna pattern and absorb microwave energy. The same is true with the temperature sensor(s) 30 in lumen 26. The result is that the catheter may heat the adjacent tissue unevenly so that some tissue is heated excessively while other tissue is not heated enough to achieve the desired thermal effect. This problem is exacerbated by the fact that the temperature sensor(s) 30 measure the temperature on or in probe 10, not the actual temperature of the tissue surrounding the probe. The upshot is that prior catheters of this type do not achieve the desired degree of temperature control of the tissue being heated.
The conventional catheters suffer also because of the presence of temperature sensing devices in the catheters. More particularly, thermisters and thermocouples require connecting wires which are prone to failure. They also reduce the catheter""s flexibility making it more difficult to thread the catheter through the urethra. On the other hand, fiberoptic sensors are fragile and quite expensive thereby increasing the overall cost of the apparatus.
Accordingly, it is an object of the present invention to provide improved transurethral microwave warming apparatus particularly adapted to treat benign prosthetic hyperplasia.
Another object of the invention is to provide such apparatus which includes a catheter able to heat the tissue to be treated relatively uniformly.
Another object of the invention is to provide apparatus of this type which can precisely monitor the actual temperature of the tissue being treated.
A further object of the invention is to provide transurethral microwave warming apparatus which accurately monitors tissue temperature without the need for thermocouples, fiberoptic circuitry or other temperature sensing hardware in the apparatus"" catheter or probe.
Yet another object of the invention is to provide a transurethral microwave catheter which is quite flexible to facilitate passage through the urethra.
A further object of the invention is to provide such a catheter which is relatively inexpensive to manufacture in quantity.
Other objects will, in part, be obvious and will, in part, appear hereinafter.
The invention accordingly comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the following detailed description, and the scope of the invention will be indicated in the claims.
Our dual mode transurethral warming apparatus includes a urethral catheter dimensioned for insertia through the urethra. The catheter includes an elongated flexible tube having a plurality of longitudinal lumens extending between the ends of the tube. A coaxial cable extends along one of the lumens to an antenna in the form of a multiturn helical winding wound around the outside of the tube. A first connector connects one of the cable conductors to one end of the winding and a second connector connects the other cable conductor to the other end of the winding so that the antenna formed by the winding is larger in diameter than the cable and all of the lumens are located within the winding.
The cable is connected to a control and display unit which includes a transmitter providing electromagnetic energy via the cable to the antenna so that the antenna generates an electromagnetic field sufficient to treat tissue adjacent to the antenna. The same antenna also detects thermal energy emitted by the tissue thereby developing an electrical signal which is fed via the cable to a receiver in the form of a radiometer in the control and display unit. As will be described in detail later, the cable is connected to the transmitter and receiver by way of a diplexer which separates the transmitter and receiver signal frequencies allowing the use of the common coaxial cable and antenna for both heating the tissue and sensing the actual temperature of the tissue.
Preferably, the catheter includes an inflatable balloon at the distal end of the tube, the balloon being inflated by flowing a gas or liquid inflation fluid to the balloon via one of the lumens in the tube. Other working lumens may be included in the tube for providing drainage and/or for coolant circulation to cool the exterior surfaces of the catheter.